Abstract

We report a fully automated mid-IR difference-frequency
spectrometer with a spectral resolution under 70 MHz pumped by a pair
of conventional room-temperature 800–900-nm diode lasers. 0.1 µW of tunable cw radiation is produced from incident-diode
powers of 120 and 75 mW. The system has computer-controlled beam
alignment with compact CCD cameras, motorized mirrors and positioners
to obtain 0.01° crystal-angle positioning, 4-µm beam overlap
at the nonlinear crystal, and automated diode laser beam
collimation. Computer-operated frequency control uses temperature
tuning and current tuning of the free-running diode lasers. The
system has been demonstrated by successfully scanning, without any
human intervention, 64 randomly selected acetylene absorption lines
between 12 and 15 µm. Spectral scans of ammonia are also
presented. This mid-IR spectrometer is suitable for fully automated
spectroscopy of an unlimited list of mid-IR frequencies and has the
potential to detect any trace gas that has an acceptable absorption
line within the large tuning range.

References

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